Known as the "iron chancellor", Gordon Brown possesses the evangelical sincerity of a Scottish puritan and at times resembles a latter-day John Knox. He became notorious during Labour's first two years in office for sticking to Conservative spending plans. Since then he has opened the government's purse strings a little while developing vast budget surpluses and spreading a little joy.

He has retained his gloomy, brooding dominance, stomping about the Treasury while shaping the nation's finances, planning his party's election strategy and plotting - perhaps - his eventual acquisition of the highest political job of all.

Mr Brown learned his oratorical mixture of Presbyterian doom and self-satisfied righteousness at the feet of his Labour-voting father, a Church of Scotland minister, who descended from Dunfermline farm labourers. At the age of 12 he volunteered to canvas against Sir Alec Douglas-Home at the 1963 Kinross and West Perthshire byelection.

His ambition was evident from the time he reached Edinburgh University, where he chaired its Labour club and became only the second student to win election as rector of its student court. By 1977, at 26, he was elected to Labour's Scottish executive and in 1983 he was elected to super-safe Dunfermline East. In the Commons he came of age in 1988 when, in the absence of John Smith, he made mincemeat of the then chancellor, Nigel Lawson.

His increasing commitment to politics suppressed his other interests, including rugby. As a schoolboy he lost the use of his left eye during a game - blighting his hope of becoming a professional footballer.

Until his 2000 marriage to public relations executive Sarah Jane Macaulay, his workaholic tendencies had hindered romance although his previous girlfriends included Sheena Macdonald, Marion Calder and Princess Margarita, the eldest daughter of exiled King Michael of Romania. She said: "It was a very solid and romantic story. I never stopped loving him but one day it didn't seem right any more, it was politics, politics, politics, and I needed nurturing."

At Labour's Brighton conference in September 2000 it became clear he is a scrooge-Santa, one who can only be "generous" in a way he dictates. Only the poorest and next-poorest pensioners can benefit from increases, says Mr Brown. Pensions cannot be linked to national income because he dislikes giving to the one-sixth of pensioners already receiving more than £20,000 annually.

His unbending belief in his own judgement has been placed under enormous pressure - as in September 2000 when he was publicly attacked by Barbara Castle MP, John Edmonds from the GMB and Rodney Bickerstaffe of Unison after he defied the wishes of the majority of Britain's 11m pensioners.

But Mr Brown's frugality has also helped him gain a praetorian guard of admirers, led by close adviser Ed Balls. These, plus the fine-tuned treasury machine, keep him in touch with complex world financial movements, helping him to avoid blunders like that of August 1992. Then, in opposition, he resisted all efforts by Labour colleagues to advocate lowering the alignment of sterling in the ERM, only to see Britain ignominiously expelled.

He can win favour as the "red chancellor" with brilliant, tongue-chewing, Tory-baiting speeches that, more often than not, manage to hit opponents in the solar plexus while also amusing his own side.

His classic hit in 1991 was sneering at the Tory finances as dependent on "a Greek millionaire moving his money out of [Greek] colonels into Majors". John Major was so upset by this baiting that he tagged him "a specialist in personal abuse."

For his career to move up another notch he must manoeuvre successfully to win allies among the rival fiefdoms which make up the Labour cabinet. He was very accomplished in building such links until Tony Blair slowly twigged that he was surrounded by Brownite allies and neutered Nick Brown, one of the chancellor's major supporters, by moving him from chief whip to agriculture minister in the 1998 reshuffle.

But Mr Brown still has Alistair Darling at social security, Clare Short at international development and Andrew Smith backing him up as chief secretary.

The biggest longterm battle that he faces concerns the euro. Although at heart a pro-European, Mr Brown was the first disciple to become ultra-cautious about the timing of joining the euro. This has since been justified by the currency's tumbling value and its rejection by the Danes. He imposed his caution on the Blair government through a typically devious manoeuvre, spelled out in Andrew Rawnsley's book, "Servants of the People."

In October 1997 Mr Brown encouraged Philip Webster, political editor of the Times, to run a story which said he did not want to enter the euro for the lifetime of the 1997 parliament, having only discussed it cursorily with the PM for five minutes. This stunt, foghorned by his spokesman Charlie Whelan down a mobile phone in a pub, was designed to outflank Mr Blair, Peter Mandelson, and Robin Cook, the foreign secretary - are all advocates of entering the euro.

Mr Brown reserves special hatred for Mr Mandelson, who switched horses from Brown to Blair in the 1994 Labour leadership campaign, following John Smith's death. Mr Mandelson, quite accurately, judged Mr Blair was more likely to radically change the party. Faced with this betrayal, Mr Brown reluctantly agreed to give Mr Blair a free run for leader, provided he was offered shadow chancellor and chancellor.

But his ambition for the top job has never waned. With Mr Mandelson now in exile on the backbenches, Mr Brown has the opportunity to gain more allies by running a good election campaign. He will use this as a platform to build a warmer relationship with the public and party staff. If he is able to secure support for his longterm succession in the country and in Millbank then he will be on his way to capturing the job he wants.

Then he'll be able to move from No 11 Downing Street to his dream house - No 10.